The invention discloses a polyolefin alloy material and a preparation method thereof. The polyolefin alloy material comprises the following components in parts by mass: 5-98.9 parts of polybutene, 1-80 parts of polyethylene and 0.1-15 parts of ethylene-butene copolymer, wherein the isotacticity of polybutene is more than 85% and the melting point of polybutene is 115-129 DEG C; the melting point of polyethylene is 130-140 DEG C; and the ethylene-butene copolymer contains ethylene-butene random copolymer and block copolymer. The preparation method is characterized by adopting a loaded titanium and/or vanadium catalyst and adopting multi-segment sequential polymerization, and specifically comprises the following steps of performing ethylene polymerization or butene-1 polymerization at first, then initiating butene-1 polymerization or ethylene polymerization, and performing ethylene polymerization or butene-1 polymerization respectively again, and so on to synthesize a polyethylene/high isotactic polybutene alloy material which is a powdery or spherical product and has the advantages of excellent shock resistance, thermal creep resistance and low shrinkage rate of polybutene, and high modulus, high surface hardness, quick shaping and the like of polyethylene.